1. Field of the Invention
This invention relates to a method for forming a silicon carbide film using a plasma CVD apparatus, and particularly to a method for forming, as an etch stop layer, a silicon carbide film and a silicon oxide film.
2. Description of the Related Art
Conventionally, in LSI devices, e.g., CPU's, memories and system LSI's, aluminum alloy has been used for metal wiring. To insulate between the metal wiring, silicon oxide films are used. In some LSI devices, fluorine-containing silicon oxide films may be used.
In recent years, to strive for speeding up LSI devices, copper having smaller electric resistance has been adopted for metal wiring. To reduce wiring capacity causing delays in electronic signals, carbon-containing silicon oxide films having a low dielectric constant have begun to be adopted.
In the LSI device having copper wiring structure, an etch stop film is used for an insulation film for the carbon-containing silicon oxide film for making grooves or holes for installing copper wiring. Because the etch stop film has a slower dry etching rate as compared with the carbon-containing silicon oxide film, a silicon nitride film, which has a function for preventing copper diffusion, has been used. In the case of the silicon nitride film, however, due to its dielectric constant of approximately 7, even if a carbon-containing silicon oxide film is used, wiring capacity in its entirety increases attributable to a high dielectric constant of the etch stop film.
Consequently, using the silicon carbide film as an etch stop film was developed as presented in U.S. Pat. No. 5,800,878. A dielectric constant of the silicon carbide film is approximately 5. The silicon carbide films are applied to LSI devices using copper wiring in combination with carbon-containing silicon oxide films, whose dielectric constant is approximately 3.
There are several different types of composition for what is generally called silicon carbide films.
One type is a silicon carbide film comprising Si, C and H. This film has a characteristic of easily absorbing oxygen and moisture. Its stress and dielectric constant change if it is left in the atmosphere. Additionally, its current leakage is high and its insulating capability is poor. A dielectric constant of the silicon carbide film is approximately from 5 to 4.5.
Silicon carbide films comprising Si, C, N and H or Si, C, O and H are disclosed in P2001-30369A1, P2002-27286A1, P2001-51445A1 and P2001-31563A1 (Published U.S. patent applications). It can be said that the silicon carbide films have low current leakage and excellent insulating capability as compared with the above-mentioned SiCH film. Particularly, an SiCOH film can achieve a dielectric constant of nearly 4 (approximately 4.2) depending on a ratio of oxygen contained.
When the carbon-containing silicon oxide film is deposited directly above Cu wiring, however, there are problems described below. FIG. 6 is a cross section of device structure using Cu wiring and a low-k film, and etch stop layers. When the film is formed in etch stop layers 50, 51 and 52, and if a carbon-containing silicon oxide film is deposited directly at points 57, 58 and 59 at which the Cu wiring and the etch stop layers contact, Cu and oxygen react, and film peeling occurs.